1. Field of the Invention
The present invention relates to a solid-state laser processing apparatus. Moreover, it relates to a laser welding process for welding overlapped steel plates, laser welding process in which the solid-state laser processing apparatus is used.
2. Description of the Related Art
Laser beams differ from ordinary light in that they exhibit extremely small diverging angles. Accordingly, laser beams can be focused to small spot diameters, and can thereby produce high energy densities. Consequently, laser beams have been utilized in various fields, such as micro-fabrication for boring printed circuit boards and welding for steel plates.
However, depending on the applications, there might arise drawbacks, because laser beams do not exhibit a uniform intensity distribution curve. Accordingly, many proposals have been made in order to improve beam qualities, for instance, as disclosed in Japanese Unexamined Patent Publication (KOKAI) No. 2002-283,085.
In conventional welding techniques using laser, special lenses, such as commercially available lens assemblies and aspherical lenses, have been used in order to make laser beams free from the influence of spherical aberration to produce beam qualities exhibiting a uniform intensity distribution curve. However, these lenses are very expensive. Moreover, the lenses require long manufacturing lead times, because they are manufactured via special manufacturing processes. Consequently, the lenses suffer from a problem in that they are less likely to be used in production lines.
In addition, in laser welding using high-quality laser beams, laser beams exhibit uniform intensity distribution curves, but the profiles show steep gradients at the edges or peripheries. Accordingly, when spaces are present between steel plates in welding overlapped steel plates, for example, the steel plates might be fused off. Consequently, fused drops might occur at the welds between the steel plates.